Field of the Invention
This invention relates to an antenna module with proximity sensing function for a communications electronic device and, more particularly, to an antenna module with proximity sensing function capable of preventing electrostatic discharge shock.
Description of the Related Art
A portable electronic device is favorable for wide users recently due to numerous advantages such as small size, convenient operation and powerful function. The most popular portable electronic device is smart phone and tablet PC, in which the tablet PC first appeared from iPad by Apple Inc. in the US and followed by more technology industries involved more resource to develop similar products and the accessories.
Due to such the electronic devices has the function of wireless communications, there is an antenna disposed therein to receive and transmit wireless signals. As shown in FIG. 8, there is an antenna module 81 disposed at a side of a tablet PC 80. If the human body approaches to the antenna module 81 when the antenna module 81 is processing a wireless reception and transmission, the human body may have an issue of absorbing radiation electromagnetic wave thus to affect the health. For this reason, rules established by Federal Communications Commission (FCC) in US and Conformite European (CE) in European Union both restrict that the Specific Absorption Rate (SAR) for the human body needs to be in a reasonable range. SAR is necessary to be lower than 1.6 W/Kg according to FCC rules and is necessary to be lower than 2.0 W/Kg according to CE rules.
In order to satisfy the abovementioned rules of SAR, the antenna module 81 of such the electronic device is designed to have a power inhibit mechanism for automatically modulating the output power when the human body approaches the antenna module 81. The power inhibit mechanism is mainly to dispose a sensor pad inside the antenna module 81 for sensing whether the human body approaches or not. As the human body is getting closer to the sensor pad, such as the user exactly hold the side provided with the antenna module 81, there will be a capacitance signal inducted in a gap between the human body and the sensor pad. The capacitance will increase as the gap become smaller and the capacitance signal will be provided to a central processing unit (CPU) to allow the CPU to output a controlling instruction according to the capacitance signal for decreasing the power of a RF amplifier of the antenna module 81 and further achieving the purpose of decreasing SAR. However, the antenna module 81 is mostly disposed at the edge of the electronic device. Such the position will be easily contacted with human body thus to be affected by electrostatic discharge (ESD) shock from the human body and thereby cause the instability of the electronic device or the damages of the components.
Please refer to FIG. 9, Taiwan patent publication No. 201240206 titled “antenna with integrated proximity sensor for proximity-based radio-frequency power control” uses an antenna structure 200 to receive and transmit a RF antenna signal and sense whether the human body approaches or not. The antenna structure 200 is connected to a ground plane by capacitors CFP, CFG, respectively. However, the disclosed structure of this invention cannot achieve the effect of preventing electrostatic discharge shock so that the electronic device may be affected to cause damages when facing an abnormal instantaneous high voltage.
Please refer to FIG. 10, US patent publication No. 2011/0012793 discloses that a sensor board 66 is connected to a capacitor 124 in parallel, and the sensor board 66 can detect whether the human body approaches or not for decreasing SAR. However, such the structure also cannot achieve the effect of preventing electrostatic discharge shock.